Wireless IC device

ABSTRACT

A wireless IC device includes a wireless IC chip arranged to process a radio signal, a power-supply circuit board that is connected to the wireless IC chip and that includes a power supply circuit including at least one coil pattern, and a radiation plate arranged to radiate a transmission signal supplied from the power-supply circuit board and/or receiving a reception signal to supply the reception signal to the power-supply circuit board. The radiation plate includes an opening provided in a portion thereof and a slit connected to the opening. When viewed in plan from the direction of the winding axis of the coil pattern, the opening in the radiation plate overlaps with an inner area of the coil pattern and the area of the inner area is approximately the same as that of opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless integrated circuit (IC) devices including wireless ICs and radiation plates. More particularly, the present invention relates to a wireless IC device used in a radio frequency identification (RFID) system.

2. Description of the Related Art

RFID systems have been developed as article management systems in recent years. In such a RFID system, a reader-writer that generates an induced magnetic field communicates with an IC tag (hereinafter referred to as a wireless IC device) that is attached to an article and that stores information by a non-contact method using the electromagnetic field to transfer information.

The wireless IC device used in an RFID system includes a wireless IC chip arranged to process a specific radio signal and a radiation plate arranged to transmit and receive the radio signal. For example, a known wireless IC device is described in WO 2007/083574.

The wireless IC device described in WO 2007/083574 includes a wireless IC chip, a power-supply circuit board on which the wireless IC chip is mounted and which includes a power supply circuit including a resonant circuit having a desired resonant frequency, and a radiation plate which is adhered to a bottom surface of the power-supply circuit board and which radiates a transmission signal supplied from the power supply circuit and receives a reception signal to supply the received reception signal to the power supply circuit. The resonant frequency of the resonant circuit in the power-supply circuit board is designed so as to substantially correspond to the frequency of the transmission and reception signals, such that the wireless IC device has very stable frequency characteristics.

Since the frequency of the radio signal transmitted and received by the radiation plate is substantially determined by the power supply circuit in the power-supply circuit board in the wireless IC device described in WO 2007/083574, the wireless IC device has very good characteristics in that the frequency of the radio signal does not significantly depend on the size and/or shape of the radiation plate. However, for example, as described in Paragraph [0020] in WO 2007/083574, the magnitude of the gain of the radio signal depends on the size and/or shape of the radiation plate. In other words, the gain varies depending on the size and/or shape of the radiation plate. However, a satisfactory configuration for successfully controlling the gain is not disclosed in WO 2007/083574.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of the present invention provide a wireless IC device which effectively controls the gain of transmission and reception signals.

A wireless IC device according to a preferred embodiment of the present invention includes a wireless IC arranged to process a specific radio signal, a power-supply circuit board that is connected to the wireless IC and that includes a power supply circuit including at least one coil pattern, and a radiation plate arranged to radiate a transmission signal supplied from the power-supply circuit board and/or to receive a reception signal to supply the reception signal to the power-supply circuit board. The radiation plate includes an opening provided in a portion thereof and a slit connected to the opening and, when viewed in plan from the direction of the winding axis of the coil pattern, the opening in the radiation plate overlaps with at least a portion of an inner area of the coil pattern.

In the wireless IC device according to a preferred embodiment of the present invention, the radiation plate preferably includes the opening provided in a portion thereof and the slit connected to the opening and, when viewed in plan from the direction of the winding axis of the coil pattern in the power-supply circuit board, the opening in the radiation plate overlaps with at least a portion of an inner area of the coil pattern. Accordingly, when a current flows through the coil pattern, a magnetic field that is excited is ideally distributed through the opening in the coil pattern. The induced magnetic field excites an induced current around the opening in the radiation plate and a difference in voltage is applied to the induced current in the slit. Accordingly, the amount and/or distribution of the induced current can be controlled by changing the length and/or width of the slit so as to control the amounts of the electric field and the magnetic field occurring over the radiation plate, thus enable effective control of the gain of the transmission and reception signals.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C include diagrams showing a wireless IC device according to a first preferred embodiment of the present invention wherein FIG. 1A is a perspective view of the entire device, FIG. 1B is a perspective view showing a state in which a wireless IC chip is mounted on a power-supply circuit board, and FIG. 1C is a perspective view showing a state in which the power-supply circuit board is mounted on a radiation plate.

FIG. 2 is a plan view showing the wireless IC device of the first preferred embodiment of the present invention.

FIG. 3 is a schematic plan view showing a main portion of the wireless IC device of the first preferred embodiment of the present invention.

FIG. 4 is a schematic perspective view showing the internal configuration of the power-supply circuit board included in the wireless IC device of the first preferred embodiment of the present invention.

FIGS. 5A to 5C include diagrams showing the principle of the operation of the wireless IC device of the first preferred embodiment of the present invention wherein FIG. 5A is a cross-sectional view, FIG. 5B is a plan view around an opening, and FIG. 5C is a plan view showing propagation to the radiation plate.

FIG. 6 is an equivalent circuit of the wireless IC device of the first preferred embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view showing a main portion of the wireless IC device of the first preferred embodiment of the present invention.

FIGS. 8A and 8B include diagrams showing a wireless IC device of a second preferred embodiment of the present invention wherein FIG. 8A is a plan view and FIG. 8B is an enlarged plan view of a modification of the second preferred embodiment of the present invention.

FIG. 9 is a schematic perspective view showing a modification of a coil pattern provided inside the power-supply circuit board.

FIG. 10 is a cross-sectional view showing a wireless IC device of a third preferred embodiment of the present invention.

FIG. 11 is a plan view showing a wireless IC device, with the power-supply circuit board omitted, of a fourth preferred embodiment of the present invention.

FIG. 12 is a plan view showing a wireless IC device, with the power-supply circuit board omitted, of a fifth preferred embodiment of the present invention.

FIG. 13 is a front view showing a state in which the wireless IC device of the fifth preferred embodiment of the present invention is attached to an article.

FIG. 14 is a perspective view showing a main portion of a wireless IC device of a sixth preferred embodiment of the present invention.

FIG. 15 is a cross-sectional view showing the wireless IC device of the sixth preferred embodiment of the present invention.

FIG. 16 is a plan view showing a first modification of the radiation plate.

FIG. 17 is a plan view showing a second modification of the radiation plate.

FIG. 18 is a plan view showing a third modification of the radiation plate.

FIGS. 19A and 19B include diagrams showing a fourth modification of the radiation plate wherein FIG. 19A is an exploded plan view and FIG. 19B is a plan view in a combined state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Wireless IC devices according to preferred embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are used to identify parts and components common to the drawings. A duplicated description of such parts and components is omitted herein.

First Preferred Embodiment

The configuration of a wireless IC device of a first preferred embodiment of the present invention will now be described with reference to FIGS. 1A to 1C. As shown in FIGS. 1A to 1C, in a wireless IC device 1, a radiation plate 3 defined by a metallic film, such as a metallic foil, for example, is provided on a support base 2, which is, for example, a printed circuit board. A power-supply circuit board 4 is mounted on the radiation plate 3. The power-supply circuit board 4 includes a power supply circuit including at least one coil pattern, and a wireless IC chip 5 arranged to process a specific radio signal is mounted on the power-supply circuit board 4. Specifically, the wireless IC chip 5 is mounted on one main surface 4 a of the power-supply circuit board 4, and the power-supply circuit board 4 is mounted on the radiation plate 3 with the other main surface 4 b of the power-supply circuit board 4 defining the mounting surface. The wireless IC chip 5 includes a clock circuit, a logic circuit, a memory circuit, and other suitable circuit elements, and necessary information is stored in the wireless IC chip 5.

As shown in FIG. 1B, multiple connection electrodes 11 via which the wireless IC chip 5 is mounted on and connected to the power-supply circuit board 4 are provided on the one main surface 4 a of the power-supply circuit board 4. The connection electrodes 11 are electrically connected to respective multiple connection electrodes (not shown) provided on the rear surface of the wireless IC chip 5 via conductive bonds 8 (see, for example, FIG. 10) such as solder, for example. As a result, the wireless IC chip 5 is mounted on the one main surface 4 a of the power-supply circuit board 4. In addition, mounting electrodes 12 via which the power-supply circuit board 4 is mounted on the radiation plate 3 are provided on the other main surface 4 b of the power-supply circuit board 4.

As shown in FIG. 1C, the radiation plate 3 includes an opening 7 provided in a portion thereof and a slit 6 connected to the opening 7. One end of the slit is connected to the opening 7 and the other end thereof opens at a side edge of the radiation plate 3. In other words, the slit 6 is arranged so as to communicate the opening 7 with the side edge of the radiation plate 3. Although the slit 6 preferably has a substantially straight shape, as in the first preferred embodiment, in terms of the workability, the slit 6 may have a meandering shape or a curved shaped.

Furthermore, multiple mounting electrodes 15 via which the power-supply circuit board 4 is mounted on and connected to the periphery of the opening 7 are provided on the radiation plate 3. The mounting electrodes 15 are preferably connected to the mounting electrodes 12 provided on the other main surface 4 b of the power-supply circuit board 4 via conductive bonds 16, such as solder, for example (see, for example, FIG. 5A). The mounting electrodes 15 are preferably defined by apertures resulting from partially striping a protective layer 14 that is coated on the surface of the radiation plate 3 and that is made of a resist material or other suitable material, for example. In other words, a portion of the radiation plate 3, which corresponds to the open portions in the protective layer 14, defines the mounting electrodes 15.

In the first preferred embodiment, the mounting electrodes 12 provided on the other main surface 4 b of the power-supply circuit board 4 are preferably not directly connected to the power supply circuit provided inside the power-supply circuit board 4. The mounting electrodes 12 are preferably connected to the mounting electrodes 15 defined by a portion of the radiation plate 3 via the conductive bonds 16, such as solder.

The radiation plate 3 preferably has a substantially planar rectangular shape, for example, as shown in FIG. 2, and the power-supply circuit board 4 on which the wireless IC chip 5 is mounted is mounted at a substantially central portion near one longitudinal side edge of the radiation plate 3. In the first preferred embodiment, for example, a ground electrode that is incorporated in an electronic device, such as a mobile phone or a personal computer, and that is provided on a printed circuit board including a certain electronic circuit may be used as the radiation plate 3. In other words, although the radiation plate 3 may be provided as a separate element having only a radiation function, ground electrodes used in various electronic circuits may alternatively be used as the radiation plate 3.

In relation to a coil pattern 23, shown in FIG. 3, provided in the power-supply circuit board 4, the opening 7 provided in the radiation plate 3 overlaps with at least a portion of an inner area of the winding path of the coil pattern 23, when viewed in plan from the direction of the winding axis of the coil pattern 23. As shown in FIG. 3, the opening 7 preferably substantially entirely overlaps with the inner area of the coil pattern 23 and the opening 7 preferably has approximately the same area as that of the inner area of the coil pattern 23. This is because magnetic fields H, shown in FIG. 5A, caused by the coil pattern 23 efficiently spread over the radiation plate 3 to suppress loss and improve the gain.

The power-supply circuit board 4 in the first preferred embodiment includes a multilayer body in which a plurality of dielectric layers preferably defined by resin layers or ceramic layers, for example, are layered. Preferably, the coil pattern 23 of the power supply circuit includes a plurality of annular electrodes arranged on the plurality of dielectric layers that are connected to one another via interlayer conductors in the layered direction in a helical pattern having the winding axis. However, the power-supply circuit board may include a coil pattern provided on a single-layer board.

As shown in FIG. 4, the power-supply circuit board 4 including the helical coil pattern 23 supplies a transmission signal from the wireless IC chip 5 to the radiation plate 3 and supplies a reception signal from the radiation plate 3 to the wireless IC chip 5.

The power supply circuit will now be specifically described. A connection electrode 11 a arranged to be connected to the connection electrode on the wireless IC chip 5 is connected to a pad conductor 22 a provided on another layer via an interlayer connection conductor 21 a provided in the multilayer body, and a wiring conductor 23 a that extends from the pad conductor 22 a and that defines a portion of the coil pattern 23 on the corresponding layer is arranged in a substantially annular shape to be connected to a pad conductor 24 a provided on the same layer. The pad conductor 24 a is connected to a pad conductor 22 b provided on another layer via an interlayer connection conductor 21 b, and a wiring conductor 23 b that extends from the pad conductor 22 b and that defines a portion of the coil pattern 23 on the corresponding layer is arranged in a substantially annular pattern to be connected to a pad conductor 24 b provided on the same layer.

Furthermore, the pad conductor 24 b is connected to a pad conductor 22 c provided on another layer via an interlayer connection conductor 21 c, and a wiring conductor 23 c that extends from the pad conductor 22 c and that defines a portion of the coil pattern 23 on the corresponding layer is arranged in a substantially annular pattern to be connected to a pad conductor 24 c provided on the same layer. The pad conductor 24 c is connected to a pad conductor 22 d provided on another layer via an interlayer connection conductor 21 d, and a wiring conductor 23 d that extends from the pad conductor 22 d and that defines a portion of the coil pattern 23 on the corresponding layer is routed in an annular pattern to be connected to a pad conductor 24 d provided on the same layer.

Furthermore, the pad conductor 24 d is connected to a pad conductor 22 e provided on another layer via an interlayer connection conductor 21 e, and a wiring conductor 23 e that extends from the pad conductor 22 e and that defines a portion of the coil pattern 23 on the corresponding layer is arranged in a substantially annular pattern to be connected to a pad conductor 24 e provided on the same layer. The pad conductor 24 e is connected to a pad conductor 22 f provided on another layer via an interlayer connection conductor 21 f, and a wiring conductor 23 f that extends from the pad conductor 22 f and that defines a portion of the coil pattern 23 on the corresponding layer is arranged in a substantially annular pattern to be connected to a pad conductor 24 f provided on the same layer. The pad conductor 24 f is connected to a connection electrode 11 b via an interlayer connection conductor 25.

In other words, the interlayer connection conductors 21 a to 21 f, the pad conductors 22 a to 22 f, the substantially annular wiring conductors 23 a to 23 f, the pad conductors 24 a to 24 f, and the interlayer connection conductor 25 define the coil pattern 23. Electrodes 11 c and 11 d are provided on the surface of the multilayer body defining the power-supply circuit board 4. The electrodes 11 c and 11 d function as mounting electrodes to mount the wireless IC chip 5 and are not connected to the coil pattern 23 provided in the power-supply circuit board 4.

As described above, in the first preferred embodiment, the radiation plate 3 includes the opening 7 provided in a portion thereof and the slit 6 connected to the opening 7. The opening 7 overlaps with the inner area of the coil pattern 23, when viewed in plan from the direction of the winding axis of the coil pattern 23 provided in the power-supply circuit board 4. In addition, the opening 7 preferably has approximately the same area as that of the inner area of the coil pattern 23. Accordingly, as shown in FIG. 5A, for example, during the transmission of a radio signal, a signal current flows from the wireless IC chip 5 to the coil pattern 23 and the induced magnetic fields H caused by the current is ideally distributed through the opening 7, as shown by broken lines in FIG. 5A. The ideal distribution of the magnetic fields H means that a center B of the two magnetic fields H coincides with the center of the opening 7. The gain of the radiation plate 3 is maximized in this state.

The induced magnetic fields H cause induced currents I1 and I2 (the propagation direction of the current I1 differs from that of the current I2 by 180 degrees) around the opening 7, as shown in FIG. 5B. Since the slit 6 is connected to the opening 7, the flows of the induced currents I1 and I2 are restricted by the slit 6 to produce a difference in voltage, i.e., to produce a capacitance. Accordingly, the amounts and/or distributions of the induced currents I1 and I2 can be effectively controlled by adjusting a length L1 and/or a width L2 of the slit 6 to control the amounts of the electric field and the magnetic field produced over the radiation plate 3. As a result, it is possible to effectively control the gain of the transmission signal.

In the radiation plate 3, the distribution of the electromagnetic field is two-dimensionally spread over the radiation plate 3 due to a linkage among the induction of the magnetic fields H by the induced currents I1 and I2, the induction of an electric field E by the magnetic fields H, and the induction of the magnetic fields H by the electric field E, as shown in FIG. 5C. The distribution of the electromagnetic field produces the transmission of the radio signal. Accordingly, it is preferable that the radio signal processed in the wireless IC device 1 be within a high frequency band, and more preferably, within a ultra high frequency (UHF) band.

As described above, the gain of the radio signal transmitted and received on the radiation plate 3 can be controlled by adjusting the length L1 and/or the width L2 of the slit 6. Specifically, the gain tends to increase when the length L1 of the slit 6 is increased and when the width L2 of the slit 6 is decreased.

As shown in FIG. 5A, it is preferable that the main portions of the mounting electrodes 12 provided on the power-supply circuit board 4 be provided in areas other than the inner area of the coil pattern 23, when viewed in plan from the direction of the winding axis of the coil pattern 23. In other words, it is preferable that the mounting electrodes 12 be arranged so as not to impede the production of the ideal magnetic fields H, particularly, so as not to impede the magnetic fields H passing through the opening 7. Furthermore, it is preferable that the main portions of the mounting electrodes 12 be provided within the plane of incidence of the coil pattern 23. Similarly, when viewed in plan from the direction of the winding axis of the coil pattern 23, the main portions of the mounting electrodes 15 toward the radiation plate 3 are preferably provided in areas other than the inner area of the coil pattern 23 and, furthermore, the main portions of the mounting electrodes 15 are preferably provided within the plane of incidence of the coil pattern 23.

As shown in FIG. 4 and FIG. 5A, the substantially annular wiring conductors 23 b to 23 f provided on the respective dielectric layers preferably include a plurality of line conductors that are parallel or substantially parallel with each other at predetermined intervals. Specifically, in the first preferred embodiment, the substantially annual-shaped wiring conductors 23 b to 23 f include two line conductors that are parallel or substantially parallel with each other and that connects the pad conductors arranged at both sides. Consequently, the magnetic flux passes between the two line conductors so to spread the excited magnetic fields toward the center of the coil pattern 23, that is, in a direction perpendicular or substantially perpendicular to the winding axis, thus allowing the magnetic flux to be efficiently used. In addition, an increase in the number of the annular conductors that are parallel or substantially parallel with each other has the advantage of decreasing the direct current resistance of the annular conductors. As a result, the gain of the radio signal is improved.

As shown in FIG. 6, the wireless IC device 1 of the first preferred embodiment includes a differential-output-type wireless IC chip 5 and is configured such that the coil pattern 23 is connected in series between two input-output electrodes. And, the induced magnetic fields H induced by the coil pattern 23 are propagated to the portion around and through the opening 7 of the radiation plate 3 in an ideal manner.

Although only the coil pattern 23 is shown as the power supply circuit in this equivalent circuit, the stray capacitance produced between the annular electrodes on the respective layers is also used as a capacitance component because the inductance of the coil pattern 23 is used as an inductance component and the coil pattern 23 is defined by the layered annular electrodes, as described above. It is sufficient for the power supply circuit provided in the power-supply circuit board 4 to include at least the coil pattern. If the power supply circuit has a particular resonant frequency, the power supply circuit may preferably further include, for example, a capacitance component and an inductance component arranged to adjust the resonant frequency.

In the first preferred embodiment, the power supply circuit in the power-supply circuit board 4 preferably has a particular resonant frequency and the frequency of the radio signal transmitted and received on the radiation plate 3 preferably substantially corresponds to the resonant frequency. The “substantial correspondence” means that the bandwidth of the resonant frequency of the power supply circuit is substantially the same as the frequency band of the radio signals that are transmitted and received on the radiation plate 3. Since the frequencies of the transmission signal and/or the reception signal are substantially the same as the resonant frequency of the power supply circuit, as described above, it is possible to provide a wireless IC device having stable frequency characteristics that do not depend on the size and/or shape of the radiation plate 3 or the shape, the material, or other characteristics of the support base 2 which supports the radiation plate 3.

In the first preferred embodiment, as shown in FIG. 7, in terms of the area of the periphery of the opening 7 in the radiation plate 3, that is, the area of the portion in which the magnetic flux induced by the coil pattern 23 is received, it is preferable that T2>T1 where T1 denotes the thickness of the coil pattern 23 in the layering direction and T2 denotes the length from a position 10 a corresponding to the outer edge of the coil pattern 23 to an outer edge 10 b of the radiation plate 3. Establishing such a relationship between the size of the periphery of the opening 7 in the radiation plate 3 and the size of the coil pattern 23 enables the magnetic flux caused by the coil pattern 23 to be received at the side of the radiation plate 3 at a high efficiency of at least about 80%, thus providing a wireless IC device having a reduced loss and greater gain.

Since the power-supply circuit board 4 is coupled to the radiation plate 3 primarily via the magnetic field in the first preferred embodiment, it is not necessary to consider the impedance matching between the power-supply circuit board 4 and the radiation plate 3. In other words, according to the first preferred embodiment, as described above, preferably designing the shape of the slit 6 enables the gain of the radio signal to be very easily controlled.

Second Preferred Embodiment

As shown in FIG. 8A, a wireless IC device 31 of a second preferred embodiment of the present invention is similar to the wireless IC device 1 of the first preferred embodiment. The wireless IC device 31 of the second preferred embodiment differs from the wireless IC device 1 of the first preferred embodiment in that a power-supply circuit board 34 is arranged along a side edge of a radiation plate 33. In the wireless IC device 31, the length, refer to as L1 in FIG. 5B, of a slit 36 extending from the side edge of the radiation plate 33 to an opening 37 is decreased and, thus, the gain tends to be decreased. In addition, as shown in FIG. 8B, the width of a slit 36′ provided in a radiation plate 33′ may be approximately the same as the width of an opening 37′.

Specific numerical values of the gain depending on the numerical value of the length L1 of the slit 36 will now be described when the radiation plate 33 has a length of about 14 cm and a width of about 4 cm.

When L1=about 0 mm, the gain is equal to about −14.4 dB.

When L1=about 0.5 mm, the gain is equal to about −13.1 dB.

When L1=about 1.0 mm, the gain is equal to about −11.6 dB.

When L1=about 1.5 mm, the gain is equal to about −10.9 dB.

When L1=about 2.5 mm, the gain is equal to about −9.4 dB.

When L1=about 4.5 mm, the gain is equal to about −7.9 dB.

In the coil pattern 23 provided in the power-supply circuit board 4, the annual conductor provided on each dielectric layer may include one line conductor, as shown in FIG. 9. The coil pattern 23 shown in FIG. 4 includes the wiring conductors 23 b to 23 f provided on the five layers whereas the coil pattern 23 shown in FIG. 9 includes the coil patterns 23 b to 23 e provided on the four layers.

When each of the annual conductors (the wiring conductors 23 b to 23 e) provided on the respective dielectric layers includes one line conductor, as in this modification, the amount of the two-dimensional distribution of the induced magnetic fields caused by the coil pattern 23 is decreased and, thus, the gain tends to be decreased as compared to the configuration shown in FIG. 4. However, the configuration shown in FIG. 9 is simplified and the size of the power-supply circuit board 4 can be reduced.

Third Preferred Embodiment

A wireless IC device 61 of a third preferred embodiment of the present invention differs from the wireless IC device 1 of the first preferred embodiment in that a radiation plate 63 is provided inside a support base 62, as shown in FIG. 10. In other words, ground electrodes provided inside the support base 62, for example, a printed circuit board, are used as the radiation plate 63.

Specifically, as shown in FIG. 10, in the wireless IC device 61, the radiation plate 63 including an opening 67 to which a slit (not shown) is connected is provided inside the support base 62. In addition, the power-supply circuit board 4 is mounted on the support base 62. The power-supply circuit board 4 includes a power supply circuit including the coil pattern 23. Furthermore, the wireless IC chip 5 arranged to process a specific radio signal is mounted on the surface of the power-supply circuit board 4.

Mounting electrodes 68 arranged to mount the power-supply circuit board 4 are provided on the surface of the support base 62. The mounting electrodes 68 are connected to the mounting electrodes 12 provided on the other main surface 4 b of the power-supply circuit board 4 via the conductive bonds 16, such as solder, for example. In addition, the mounting electrodes 12 on the power supply circuit board 14 are not directly connected to the power supply circuit provided inside the power-supply circuit board 4. Similarly, the mounting electrodes 68 on the support base 62 are not directly connected to the radiation plate 63 provided inside the support base 62.

Fourth Preferred Embodiment

A wireless IC device 71 of a fourth preferred embodiment of the present invention is a tag-type (inlay-type) wireless IC device, as shown in FIG. 11. Specifically, the wireless IC device 71 includes a radiation plate 73 preferably defined by a flexible metallic film, such as a metallic foil, for example, that is provided on a flexible support 72, such as a polyethylene terephthalate (PET) film, for example. The radiation plate 73 includes a peripheral portion of an opening 77 to which a slit 76 is connected, that is, a substantially planar portion 78 in which the magnetic flux induced by the coil pattern in the power-supply circuit board is received and meandering portions 79 in which a radio signal is primarily transmitted and received. However, no clear boundary is provided between the planar portion 78 in which the magnetic flux is received and the meandering portions 79 in which the radio signal is transmitted and received. As in the wireless IC device 1 of the first preferred embodiment, mounting electrodes 75 via which the power-supply circuit board is mounted are provided around the opening 77 by partially striping a resist material. The wireless IC device 71 can preferably be attached to various commercial products and can be used for management of distribution histories of the commercial products.

As described above, in the wireless IC devices according to preferred embodiments of the present invention, the support which supports the radiation plate may be not only a rigid board, such as a printed circuit board, for example, but may also be a flexible support 72 such as a PET film, for example, as described in the fourth preferred embodiment. Similarly, the radiation plate itself may be not only a rigid plate, such as a sintered metal or a metal plate, for example, but also a flexible plate, such as a metallic foil, for example. In addition, a portion of a metal article, such as a metallic frame of a pair of glasses or a ring, for example, may be used as the radiation plate.

Fifth Preferred Embodiment

In a wireless IC device 81 of a fifth preferred embodiment of the present invention, a radiation plate 83 defined by a metallic foil or other suitable material, for example, is provided on a relatively small support 82 defined by a flexible film or other suitable material, as shown in FIG. 12. The wireless IC device 81 preferably has a patch shape, for example. The radiation plate 83 includes an opening 87 and a slit 86 connected to the opening 87.

As shown in FIG. 13, the wireless IC device 81 is preferably used in a state in which the support 82 is adhered on an article 89. If the support 82 has a thickness that allows the magnetic flux to pass therethrough, the article may preferably be made of metal.

Sixth Preferred Embodiment

In a wireless IC device 91 of a sixth preferred embodiment of the present invention, mounting electrodes 12 a and 12 b connected to the coil pattern 23 via interlayer connection conductors 26 a and 26 b are provided on the rear surface of the power-supply circuit board 4 and the mounting electrodes 12 a and 12 b are connected to mounting electrodes 15 a and 15 b on the radiation plate 3 via the conductive bonds 16, such as solder, for example, as shown in FIGS. 14 and 15. The mounting electrodes 15 a and 15 b are defined by apertures resulting from partially striping a resist material coated on the surface of the radiation plate 3, as in the mounting electrodes 15 described in the first preferred embodiment. The configuration of the wireless IC device 91 is otherwise substantially the same as that of the first preferred embodiment.

In other words, in the sixth preferred embodiment, not only the coil pattern 23 in the power-supply circuit board 4 is electromagnetically coupled to the radiation plate 3, but also the coil pattern 23 in the power-supply circuit board 4 is directly connected (coupled) to the radiation plate 3. Accordingly, the gain of the radiation plate 3 is increased.

Meanwhile, if a plurality of wireless IC devices that have substantially the same configuration and that each include a relatively large radiation plate are laid over one another, the radiation plates tend to block the magnetic flux. In such a state, the transmission and reception between the wireless IC devices and a reader-writer is disabled. Accordingly, first to fourth modifications of the radiation plate which includes an aperture so that the magnetic flux can pass through the wireless IC devices even if the plurality of wireless IC devices are laid over one another are shown in FIGS. 16 to 19. The arrangements of the apertures shown in the first to fourth modifications in the radiation plates enable the magnetic flux to pass through the aperture even when a plurality of wireless IC devices are laid over one another, thus enabling communication with the reader-writer. In addition, the presence of the annular electrodes increases the area of a portion where the magnetic flux is received on the radiation plate to improve the gain as an antenna.

A radiation plate 100 of a first modification, shown in FIG. 16, includes a first electrode 101 including an opening 107 over which the power-supply circuit board 4 is mounted and a slit 106, and an annular second electrode 108 surrounding the first electrode 101. The radiation plate 100 is preferably defined by a metallic foil or other suitable material, for example. The first and second electrodes 101 and 108 are integrally provided on one plane and are electrically connected to each other via a connection portion 102. In the first modification, the magnetic flux passes through an aperture 109 surrounded by the annular second electrode 108. It is preferable that the opening 107 over which the power-supply circuit board 4 is mounted is arranged at a central portion of the annular second electrode 108. This configuration enables the power-supply circuit board 4 to evenly receive the magnetic flux.

A radiation plate 110 of a second modification, shown in FIG. 17, includes a first electrode 111 including an opening 117 over which the power-supply circuit board 4 is mounted and a slit 116, and an annular second electrode 118 surrounding the first electrode 111. The radiation plate 110 is preferably defined by a metallic foil or other suitable material, for example. The first and second electrodes 111 and 118 are integrally provided on one plane and are electrically connected to each other via connection portions 112 and 113. Since the first electrode 111 is connected to the annular second electrode 118 at two positions, as described above, an electrical signal caused by the magnetic field is efficiency transmitted to the power-supply circuit board 4. In the second modification, the magnetic flux passes through apertures 119 surrounded by the annular second electrode 118.

A radiation plate 120 of a third modification, shown in FIG. 18, includes a first electrode 121 including an opening 127 over which the power-supply circuit board 4 is mounted and a slit 126, and an annular second electrode 128 surrounding the first electrode 121. The first and second electrodes 121 and 128 are integrally provided on one plane and are electrically connected to each other via a connection portion 122. In the third modification, the magnetic flux passes through apertures 129 surrounded by the annular second electrode 128.

In a radiation plate 130 of a fourth modification, shown in FIG. 19, a first electrode 131 is provided separately from a second electrode 138 and the first electrode 131 is adhered on the second electrode 138. Either of a non-conductive adhesive and a conductive adhesive, for example, may preferably be used for the adhesion. In addition, the first electrode 131 may be adhered on the second electrode 138 so that the first electrode 131 opposes the second electrode 138 or so that the film having the first electrode 131 provided on its surface opposes the second electrode 138. The magnetic field is propagated even if the electrode 131 is adhered on the electrode 138. The first electrode 131 includes an opening 137 over which the power-supply circuit board 4 is mounted and a slit 136. The second electrode 138 has the same or substantially the same shape as in the second modification. The magnetic flux passes through apertures 139 surrounded by the second electrode 138. In the fourth modification, making the opening and the slit in the second electrode 138 larger than the opening 137 and the slit 136 in the first electrode 131 enables the opening 137 of a predetermined size and the width of the slit 136 to be ensured in the first electrode 131 even if a slight positional shift occurs in the adhesion of the first electrode 131 on the second electrode 138.

The wireless IC devices according to preferred embodiments of the present invention are not restricted to the preferred embodiments described above and may be varied within the scope of the summary of the present invention.

As described above, preferred embodiments of the present invention are useful for a wireless IC device and, particularly, are excellent in that the gains of transmission and reception signals can be effectively controlled.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. A wireless integrated circuit device comprising: a wireless integrated circuit arranged to process a radio signal, and a radiation plate connected to the wireless integrated circuit, the radiation plate together with the wireless integrated circuit defining a communication device for an RFID system; wherein the wireless integrated circuit is connected to a power-supply circuit including at least one coil pattern; the radiation plate includes a first electrode including an opening provided in a portion thereof and connected to an outer edge thereof and, when viewed in a direction of a winding axis of the at least one coil pattern, the opening in the first electrode overlaps with at least a portion of an inner area of the coil pattern; and the radiation plate further includes a second electrode including an opening provided in a portion thereof and connected to an outer edge thereof, and the opening in the second electrode overlaps with at least a portion of the opening of the first electrode when viewed in the direction of the winding axis of the at least one coil pattern.
 2. The wireless integrated circuit device according to claim 1, wherein a size of the second electrode viewed in the direction of the winding axis of the at least one coil pattern is larger than that of the first electrode.
 3. The wireless integrated circuit device according to claim 1, wherein the first electrode is connected to the second electrode in a conductive state or coupled to the second electrode in a non-conductive state.
 4. The wireless integrated circuit device according to claim 1, wherein the at least one coil pattern is directly connected to the radiation plate.
 5. The wireless integrated circuit device according to claim 1, wherein, when viewed in the direction of the winding axis of the at least one coil pattern, the openings in each of the first electrode and the second electrode substantially entirely overlaps with the inner area of the coil pattern and an area of the opening in each of the first electrode and the second electrode is approximately the same as that of the inner area.
 6. The wireless integrated circuit device according to claim 1, wherein the power supply circuit has a resonant frequency and frequencies of at least one of a transmission signal and a reception signal substantially correspond to the resonant frequency.
 7. The wireless integrated circuit device according to claim 1, wherein the first electrode is adhered on the second electrode. 